JPS6147981B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is applicable to pump-turbines, particularly in the area of water turbines.
This paper relates to a guide vane closing method for a high-head pump-turbine, which requires the following characteristics.

[Conventional technology]

In general, the runners and other equipment of pump turbines, particularly high head pump turbines, are designed to provide sufficient centrifugal pumping action to obtain high head during pump operation.

However, this design adversely affects the turbine operation of the pump turbine. In particular, it is considered inevitable that a characteristic called the S-shaped characteristic, which will be described later, is accompanied.
When the characteristics of the pump-turbine adopted in this design are shown by a characteristic curve representing the relationship between the number of revolutions per unit head (N ₁ ) and the flow rate per unit head (Q ₁ ) under a predetermined guide vane opening, This characteristic curve shows that in the turbine operation region, Q ₁ increases with increasing value of N ₁
has a first part in which the value of Q1 decreases, and a second part in which the value of _Q1 decreases as the value of _N1 decreases. For convenience of explanation, the second portion is referred to as an S-shaped characteristic portion in this specification. Furthermore, the characteristics of the pump turbine in the S-shaped characteristic part are hereinafter referred to as S.
These are called character characteristics. When operating a water turbine in an S-shaped characteristic section, the torque per unit head (T ₁ ) is also
It decreases as the number of revolutions per unit head (N ₁ ) decreases.

Normally, the operation of the pump-turbine is carried out in the first part. However, if the number of revolutions per unit head (N ₁ ) suddenly increases greatly due to load interruption or load reduction, the pump-turbine will be operated in the S-shaped characteristic portion. When operation in the S-shaped characteristic part starts,
The operating point of the pump-turbine follows the S-shaped characteristic part from one end to the other, and first the flow rate per unit head (Q ₁ ) and the number of rotations per unit head (N ₁ ) decrease.
After that, Q ₁ and N ₁ increase while tracing the S-shaped characteristic part in the opposite direction, like a pendulum swinging back. S
This reciprocating motion in the character characteristic portion continues almost permanently as long as the guide vane opening remains above a predetermined value, and will not end unless special measures are taken. During this period, the torque per unit head (T ₁ ) also repeatedly decreases and increases.

It is desirable to operate the pump-turbine to avoid the S-shaped characteristic part as much as possible. because,
Operation in the S-shaped characteristic section can cause abnormal water pressure fluctuations, including large water pressure rises and large water pressure drops, in the penstock and draft tube, as well as in the pump turbine itself, and may even result in water column separation. This is because the timing of entry into the S-shaped characteristic part is difficult to predict in advance due to the influence of the waterway and other units sharing the waterway. The above-mentioned load disconnection can occur, for example, when a generator connected to a pump-turbine is opened, or when an accident occurs in a device such as a transformer between the generator and the power grid, causing the generator to lose its load. This occurs when you lose your body. Water hammers can also be used when the penstock or draft tube, or both, are long.
Particular attention should be paid to intenseness.

The characteristics of a pump water turbine having S-shaped characteristics in the water turbine operation region are shown in FIGS. 1A and 1B.
In FIG. 1A, the characteristics of the pump-turbine are shown as the relationship between the number of revolutions per unit head (N ₁ ) and the flow rate per unit head (Q ₁ ), using the guide vane opening as a parameter. On the other hand, in FIG. 1B, the characteristics of the pump-turbine are shown as the relationship between the number of rotations per unit head (N ₁ ) and the torque per unit head (T ₁ ) using the same parameters.
N ₁ , Q ₁ and T ₁ are expressed by the following equations.

N ₁ = N/√, Q ₁ = Q/√, T ₁ = T/H In the above equation, the symbols N, Q, H, and T indicate the rotation speed, flow rate, effective head, and torque of the pump-turbine, respectively. .

Characteristic curves 1 and 1' are obtained under certain relatively large guide vane openings. Characteristic curves 2 and 2' are obtained under smaller guide vane openings. Characteristic curves 3 and 3' are also obtained at smaller guide vane openings.

In the a-d-h portion of characteristic curve 1, Q ₁
The value of decreases as _N1 decreases. As mentioned above, this curved portion a-d-h is referred to as an S-shaped characteristic portion in this specification. Similarly, curve portion bei is an S-shaped characteristic portion of characteristic curve 2, and curve portion cfj is an S-shaped characteristic portion of characteristic curve 3. As is clear at first glance, the S-shaped characteristic portions a-d-h of the characteristic curve 1 are longer than the S-shaped characteristic portions b-e-i of the characteristic curve 2; -i is longer than the S-shaped characteristic portion cfj of characteristic curve 3. This means that as the guide vane opening becomes smaller, the length of the S-shaped characteristic portion becomes shorter.

As in FIG. 1A, in FIG. 1B the curved sections a′-d′-h′, b′-e′-i′ and
―
f'-j' are the S-shaped characteristic portions of characteristic curves 1', 2' and 3', respectively.

FIG. 1B is closely related to FIG. 1A. For example, Q ₁ =Q _1x , N ₁ =N _1x on curve 3 in Figure 1A
The point x that satisfies the above corresponds to the point x' on the curve 3' in FIG. 1B. Point x' is T ₁ = T _1x ', N ₁ = N _1x
'(=N _1x ). Similarly, points a, b, c, d, e, f, h, i and j in FIG. 1A correspond to points a', b', b', and j in FIG. 1B, respectively.
Corresponds to c′, d′, e′, f′, h′, i′ and j′.

Curve nr is a no-load flow rate curve. curve 1,
The intersection points α, β, and γ between curves 2 and 3 and the curve nr correspond to the intersections α′, β′, and γ′ between the curves 1′, 2′, and 3′, and the straight line T ₁ =0, respectively.

Next, referring to characteristic curves 1 and 1', the operation of the pump turbine (power generation operation) will be explained. As mentioned above, the characteristic corresponding to characteristic curve 1 1' is obtained when the guide vane opening degree is set to a relatively large value. Normally, the operation of a pump-turbine is as follows:
The upper part of the characteristic curve 1, that is, the S-shaped characteristic part a-
This is done in the curved section above dh. However, if, for example, the load applied to the pump-turbine is suddenly lost, the number of revolutions (N) of the pump-turbine increases rapidly, and the value of N ₁ also increases rapidly. Thus, the pump turbine begins to operate in the S-characteristic section. During operation in the S-characteristic section, when the value of N ₁ decreases due to a decrease in the rotation speed (N) of the pump-turbine, the value of Q ₁ also decreases. Assuming that the value of H is constant, Q ₁
A decrease in the value of Q means a corresponding decrease in the pump turbine flow rate (Q). In reality, H
The value of , that is, the head difference between the pump-turbine inlet connected to the penstock and the pump-turbine outlet connected to the draft tube, increases simultaneously with a decrease in the flow rate Q.
In this way, once the value of N ₁ decreases, the flow rate Q decreases, and a decrease in the flow rate Q results in an increase in the effective head H of the pump-turbine. This increase in effective head H results in a further decrease in N ₁ , which in turn results in a further decrease in _{Q 1 .} In this way, once the operation in the S-shaped characteristic section begins, Q ₁ and N ₁
is the S-shaped characteristic part in the _Q1 decreasing direction, that is, point a
While tracing the direction from point d to point d, the acceleration decreases continuously. It can be seen that Q ₁ and N ₁ decrease at an accelerated rate and continuously, as in the positive feedback control circuit.

When the operating point of the pump-turbine finishes tracing the S-shaped characteristic part from point a to point h, the above phenomenon is gradually alleviated in the same way as in the negative feedback control circuit, and then reversed, eventually changing the S-shaped characteristic part to Q. _1, in the increasing direction, that is, from a point a little past point h to point a. Tracing the S-shaped characteristic portion in the opposite direction is also performed in the same manner as the arrow positive feedback control circuit.

While the pump turbine is operated in the S-shaped characteristic section,
The above reciprocating motion is repeated almost permanently.
As explained above, such operation is undesirable. This is because hydropower plants cause abnormal water pressure changes in each waterway system connection, and these water pressure changes result in severe water hammer and sometimes even water column separation phenomena.

It should be noted that these adverse effects associated with driving in an S-shaped section are reduced as the length of the S-shaped section is reduced. For example, if the guide vane opening is made smaller, the S-shaped characteristic part b-
If the pump-turbine is operated according to characteristic curve 2 with ei, the negative effects associated with S-characteristics are reduced.

The operation of the pump-turbine in the S-shaped characteristic portion also has an adverse effect on the torque T of the pump-turbine. When the value of N ₁ decreases in the S-shaped characteristic part, Fig. 1B
As shown in , the value of T ₁ decreases. Now again points a and h on the characteristic curve 1 shown in FIG.
is the point a' on the characteristic curve 1' shown in Figure 1B.
It must be noted that each corresponds to d′.

Assuming that the effective head H is constant, a decrease in T ₁ means a decrease in the pump turbine torque T. Furthermore, it is clear that a decrease in the pump-turbine torque T results in a decrease in the pump-turbine rotational speed N. When the pump-turbine rotation speed N decreases, correspondingly
N ₁ will decrease and then T ₁ will decrease further. In reality, during this period, as mentioned above, the effective head H
This accelerating trend will become even stronger as the number of
In this way, the pump-turbine has the characteristic curve 1
While tracing Q ₁ in the decreasing direction, the characteristic curve 1' is at the same time
This means that we are tracing from a' to point h'. The way to trace this is the same as in the case of a positive feedback control circuit.
Thereafter, when the direction of tracing the S-shaped characteristic portion is reversed, the characteristic curve 1' traces from point h' to point a'. Obviously, torque variations as described above are disadvantageous.

Now, let us consider a pump-turbine that is arranged so that the pipe on the lower pond side or the upper pond side merges with another water turbine or pump-turbine, and the pipes beyond this junction are shared. If multiple water turbines or pump-turbines sharing a pipeline do not have S-shaped characteristics, the most severe condition is where the water pressure in the upper basin side pipeline is the highest and the lower basin side pipeline water pressure is the lowest. This occurs when multiple water turbines or pump turbines are unloaded or stopped at the same time.

However, if a plurality of pump turbines having S-shaped characteristics are included in the plurality of pump turbines, simultaneous breakage is not necessarily the most severe condition due to this synergistic effect. Now, assuming that two pump-turbines sharing the upper pond side pipeline are cut off due to load, the guide vanes are closed as shown in Figure 3 due to insufficient initial rapid closure, and as a result, the guide vanes are closed as shown in Figure 3. From the maximum water pressure on the upstream side of the guide vane that occurs during initial rapid closing,
An example of the calculation results in the case where the maximum value of the water pressure on the upstream side that naturally reaches the S-shaped characteristic immediately after the rotation speed starts to decrease becomes higher is shown by a solid line in FIG. In FIG. 6, the vertical axis shows the maximum water pressure value generated in the upper pond side pipe, and the horizontal axis shows the time difference between the load shedding of the first and second units. As is clear from the solid line in this figure, the maximum water pressure value increases as the time difference increases, compared to the case where the time difference is 0 seconds, that is, simultaneous disconnection, and reaches the maximum value when the time difference is 4 seconds. If the maximum water pressure value that appears changes depending on the time difference in this way, it is necessary to perform computer analysis of many cases using the time difference as a parameter in order to determine the true maximum value at the design stage. Furthermore, even at the testing stage, in order to determine the true maximum value, it is necessary to conduct actual loading and disconnection tests for numerous cases in which the time difference is used as a parameter. These computer analyzes and load/disconnection tests not only take time, but also require the actual load/disconnection tests to be performed many times, creating a maze for the power system and causing damage to the pump-turbine or generator-motor itself. may hasten the

By the way, in the past, the method of closing the guide vanes of each water turbine or pump water turbine was determined without recognizing the existence of the abnormal synergistic effect due to the above-mentioned S-shaped characteristic.

Various methods as shown in FIG. 2 are conventionally known as methods for closing the guide vanes when the water turbine load suddenly decreases or the water turbine load is interrupted.

Figure 2 a shows that the flow rate of the water turbine decreases as the rotation increases.
Assuming the usual specification that if it decreases, it will increase,
No consideration is given to the reverse characteristics unique to high-head pump turbines, ie, S-shaped characteristics, as described above. In other words, focusing on the fact that the rotational speed of the pump-turbine increases after the load is interrupted, the rotational speed is increased while avoiding the closing operation of the guide vanes as long as the rotation continues to increase, taking into consideration only the decrease in the flow rate of the pump-turbine due to this increase in rotation. In order to prevent the flow rate reduction effect caused by the flow rate reduction effect caused by the guide vane from overlapping, that is, the guide vane is closed while the rotation speed is rising, but in reality, the rotation speed exceeds the maximum value and begins to fall. It is only after this point that the operating point enters the S-shaped region, at which point the flow rate suddenly decreases. Based on this fact, a gradual closure should have been carried out here, but in reality, a sudden closure would have begun. In this respect, it cannot be used for pump turbines with S-shaped characteristics.

b is more aggressive than a, and is designed to open the guide vane while the rotation speed is increasing to offset the decrease in flow rate due to the increase in rotation with the increase in flow rate due to the opening operation of the guide vane, and of course cannot be applied to S-shaped characteristics. .

d is set to be fast at first, and when the water pressure fluctuation value becomes large, it is stopped midway in order to prevent further increase. This is a method that is widely adopted regardless of the presence or absence of S-shaped characteristics. However, it is unclear what will happen to the maximum water pressure value in the pipeline when multiple pump turbines are no longer loaded using this closure method.

In addition, c is the closest example to the present invention shown in Japanese Patent Publication No. 49-40902, but as is clear from the description in this publication, ∂Q/∂N (where Q is the flow rate of the water turbine and N is the number of revolutions) ) specifies that the turbine closes slowly in a region where ∂Q/∂N takes a large negative value, and does not mention the S-shaped characteristic region where ∂Q/∂N is positive, which should be considered the most problematic. Of course, no consideration has been given to the loading of multiple pump-turbines sharing a pipeline or the method for closing the guide vanes in the event of a disconnection.

[Problem that the invention seeks to solve]

In addition, in the closing methods shown in c and d, there is no guideline as to the rapid closing speed of the guide vanes immediately after the load is cut off, or the closing opening degree, so it is difficult to use model or actual water turbines. They tried closing the guide vanes in various patterns and found the optimal pattern based on the increase in water pressure when they were closed. However, in the case of multiple pump-turbines sharing a pipeline, water pressure fluctuations may be different from those of other pattern-turbines. In order to find the optimal pattern, shear tests had to be performed for all cases.

The present invention has been made in view of the above circumstances, and its purpose is to maintain the upper pond side pipeline even if a plurality of pump turbines sharing the pipeline are loaded or disconnected under any conditions. An object of the present invention is to provide a method for closing a guide vane in which the water pressure generated in the guide vane does not become excessive.

[Means of solving the problem]

The above objective is based on the case where the load is cut off from the rated load of one pump-turbine, and at this time, the maximum water pressure value due to entering the S-shaped characteristic region immediately after the rotation starts to decrease, and the maximum water pressure value immediately after the load stops. This is achieved by setting the load, the rapid closing speed of the guide vane immediately after disconnection, and the closing opening degree so that the values are approximately equal.

[Effect]

The characteristic of closing the guide vanes of a single pump-turbine is that when the guide vanes close in the pattern shown in Figure 3, the water pressure on the upper pond side is faster when the load reaches the S-shaped region, and the guide vanes close more quickly immediately after the load breaks. Although it is higher than the water pressure at the rear (indicated by the guide vane servo motor stroke), the rapid closing speed immediately after the load is disconnected, and
By closing the guide vanes to the low opening range,
Immediately after loading and unloading, the water pressure increases, and the water pressure in the S-shaped area decreases. By adjusting the quick closing speed and the closing opening degree, ΔH ₁ and ΔH ₂ become approximately equal values as shown in FIG. At this time, both ΔH ₁ and ΔH ₂ become smaller than the maximum value of the water pressure on the upper pond side in FIG.
This is because the closing method shown in Figure 5 closes the guide vanes to a greater degree immediately after the load is cut off (that is, the guide vanes are closed to a low opening), so when entering the S-shaped region, This is because the guide vane opening degree is small, so the influence of the S-shaped characteristic becomes small.

If the closing method shown in Figure 5 is adopted, and if multiple pump turbines are loaded and disconnected at the same time or at different times, the water pressure on the upper pond side will be at its maximum due to mutual interference. , in the case of simultaneous termination. In other words, this is a case where the mutual load on the pump-turbine and the water pressure rise ΔH ₁ immediately after the cut-off occur simultaneously, and if we analyze this simultaneous case, we get:
In the case of other time lags or breaks, the increase in water pressure will not be greater than if the breaks occur at the same time.

Therefore, when the load is removed from the rated load in standalone operation, the upstream water pressure increase ΔH ₁ immediately after the load is removed and the upstream water pressure increase ΔH ₂ that occurs when the load enters the S-shaped region is approximately equal. By setting the closing speed and closing opening of the guide vanes immediately after loading or disconnection, and adopting a method in which the guide vanes are rapidly closed to these speeds and openings, and then closed slowly, it is possible to control how multiple pump-turbines operate. Even if the load is applied or disconnected under such conditions, the increase in water pressure on the upstream side will not become excessive.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. As is clear from the figure, the initial closing speed of the guide vane (guide vane) is increased, the closing width is increased, and the opening is suddenly closed to a smaller opening than the conventional example shown in Figure 3. The side water pressure increase ΔH ₁ is made higher than the water pressure increase ΔH ₂ on the upstream side of the water turbine that occurs after entering the S-shaped region. Correspondingly, the width of the water pressure drop on the downstream side of the water turbine is also larger when ΔH ₁ , and smaller when ΔH ₂ . The initial closing stage of the guide vanes will be explained in more detail as follows. When a load or disconnection occurs, the rotational speed increases, and the governor (not shown) operates to close the guide vanes with full force. The limit value of the displacement of the plunger of the pressure regulating valve is set to a large value only during the initial closing immediately after the load is disconnected, and thereafter the guide vane is closed to a predetermined opening (or other known judgment conditions). ) to automatically switch the limit value of the pressure regulating valve plunger to a small value. Thus, the initial confinement speed is fast;
After that, the closing speed becomes slower, resulting in a bent state as shown in the figure. As mentioned above, since the width of the initial confinement is made larger than before, the size of the subsequent S-shaped characteristic curve can be further compressed, resulting in ΔH ₂
has become that much smaller. As a result,
When multiple pump-turbines sharing a pipeline are simultaneously unloaded and disconnected, the maximum water pressure increase on the upstream side of the turbine is:
It is exactly at the time of ΔH ₁ , and this value is higher than the water pressure increase value that occurs during any time lag or disconnection.
In order to find the initial confinement speed and confinement width at which ΔH ₁ and ΔH ₂ are approximately equal according to the characteristics shown in Figure 5, experiments are carried out by varying the initial confinement speed and confinement width during independent operation of the pump-turbine. It is obtained by measuring ΔH ₁ and ΔH ₂ . In particular, ΔH ₁ is
Since the faster the initial closing speed and the larger the closing width, the larger the closing width is, the initial closing speed and closing width such that ΔH ₁ =ΔH ₂ can be found through several experiments.

Furthermore, in Figure 5, the guide vanes are quickly closed again after escaping from the S-shaped area, but this is done in order to prevent the ship from entering the S-shaped area again due to the subsequent swing-back action of water pressure. . However, even if the gradual closing continues as shown by the two-dot chain line, and the water pressure swings back to enter the S-shaped region again, the guide vane opening should have become considerably smaller at that time, and the size of the S-shaped characteristic will be correspondingly large. , so there is no need to worry about larger fluctuations than the water pressure values experienced up to that point.

By the way, as is clear from FIG. 1, the S-shaped characteristic occurs at the point where the torque becomes approximately zero, which is the point at which the rotational speed stops increasing and begins to decrease.

Therefore, it is simple and effective to close the guide vanes early before the rotational speed reaches its maximum value, that is, while it is outside the S-curve.

[Effects of the Invention] According to the present invention, the water pressure value generated in the upper pond side pipe becomes the maximum when there is a simultaneous power outage, and this makes it possible to analyze and test water pressure value fluctuations targeting time differences and power outages. It is possible to provide a guide vane closing method that is completely unnecessary and does not cause an excessive rise in water pressure on the upstream side.

[Brief explanation of the drawing]

Figure 1A is a flow rate characteristic (N ₁ - Q ₁ ) graph of a pump-turbine with S-shaped characteristics. Figure 2B is also a torque characteristic (N ₁ -T ₁ ) graph. Figures 2 a to d are graphs of conventional loads. Figure 3 is a diagram showing the method of closing the guide vanes in the event of a blowout, Figure 3 is a diagram showing the dynamic characteristics of a pump-turbine when the conventional guide vane closing method is adopted, and Figure 4 is a diagram showing the conventional technology such as Figure 3. Fig. 5 is a diagram showing the dynamic characteristics of a pump-turbine when using the guide vane closing method showing one embodiment of the present invention, and Fig. 6 is a diagram showing the present invention and the prior art. FIG. 2 is a comparison diagram of the maximum water pressure value generated in the upstream pipe line. N... Number of revolutions, H... Effective head, Q... Turbine flow rate, T... Turbine torque, N ₁ ... Rotation speed per unit head, Q ₁ ... Water turbine flow rate per unit head, T ₁ ...
...Hydraulic turbine torque per unit head.

Claims (1)

[Scope of Claims] 1. A water turbine having a plurality of pump-turbines arranged so that the pipe on the lower pond side or the upper pond side merges with other water turbines or pump-turbines and sharing the pipes beyond this merging point; Each of the pump-turbines has an S-shaped characteristic, the so-called (However, N is the rotation speed and H is the effective head.) As N ₁ decreases in a relatively high range, Q ₁ = Q/√
(where Q is the flow rate of the water turbine) and T ₁ = T/H (where T is the generated torque of the water turbine) has the characteristic of decreasing, and when an individual pump-turbine is disconnected from the load during power generation operation, the guide vanes In a pump-turbine guide vane closing method in which the guide vanes are closed rapidly and then transitioned to slow closure at least once, the closing speed and closing width for rapidly closing the guide vanes are the same as those rated when the pump-turbine is operated independently. Immediately after the load is removed or removed, the rotation speed of the pump-turbine reaches its maximum value, and immediately after the rotation speed begins to decrease, it automatically restarts by entering the S-shaped characteristic while continuing the gradual closure described above. A method for closing a guide vane of a pump water turbine, characterized in that the rising water pressure on the upstream side of the guide vane is made to approximately match the rapid closing speed and closing width of the guide vane which are approximately equal to the maximum water pressure during the rapid closing. .